desktop-packages team mailing list archive
-
desktop-packages team
-
Mailing list archive
-
Message #111169
[Bug 1436595] Re: Images too bright
** Attachment added: "comparison.png"
https://bugs.launchpad.net/ubuntu/+source/eog/+bug/1436595/+attachment/4366255/+files/comparison.png
--
You received this bug notification because you are a member of Desktop
Packages, which is subscribed to eog in Ubuntu.
https://bugs.launchpad.net/bugs/1436595
Title:
Images too bright
Status in eog package in Ubuntu:
New
Bug description:
Most images have their values shifted upwards when displayed in eog,
and I don't think it is intentional. Reporting this as a bug is
complicated because I am not sure if some programs, such as eog,
change their display of an image based on screen settings for
colorspace or gamma. I am not an expert on graphics, but something
does seem to be wrong.
So at least for my computer, eog seems to stretch out the range just
above a 0 value. A very dark area will have a clear contrast between
the totally black pixels, with a value of zero, and the ones just
above it. In one image I tested, eog did not display any pixels with a
value in the range of 1 to 5, as in the histogram of a screenshot of
eog's display of the image.
In comparison, a screenshot of Firefox's display of the same image had
numerous pixels in the 1~5 range. The GIMP image editor displayed this
image the same as Firefox, with the histogram showing that the pixels
were being displayed without any adjustment.
Basically, if a lot of different programs display things differently
and inconsistently, some of them have to be wrong, and it seems likely
that eog is. Due to inconsistencies, I'm not actually sure what is the
correct, or the best way to display images, which might be different
from the correct way.
Programs used to test, convert, and display images:
imagemagick
ffmpeg (for conversion) and avplay (for display, since ffplay isn't provided on my distribution)
eog
Firefox
vlc
GIMP
I thought Firefox was displaying non-stripped pngs the same as eog
does, but it's actually slightly different. While gray areas are about
the same as eog, red areas are slightly darker in Firefox.
A description of how various programs display images:
vlc seems to be the same as avplay, and both are different from either Firefox or eog. Dark red is a bit more like brown or orange, while contrast for luminosity or luminance (?) seems to be higher; I am just noting that it is different. This is for a png image.
I thought eog was displaying all images the same way, until I
encountered a png that worked differently. I thought eog was
displaying this png without any adjustments, as it's slightly darker
than how eog displays other pngs, but it's actually slightly darker
with more intense colours than how other programs display the same
image. But for all other images, eog seems to make them slightly
brighter.
Firefox displays jpgs without any adjustment, but most pngs are
slightly brighter. As described, this is slightly different than how
eog makes images brighter. If an image is converted with -strip action
in imagemagick, Firefox shows the png without adjustments. A png
output from ffmpeg is also displayed without adjustments. It seems to
be related to the 'png:sRGB : intent=<value>' property but that would
be a Firefox bug. It's relevant because it seems to adjust the display
of images in a way that's similar to eog, though still different. If a
stripped png is converted again without applying the -strip action
again, Firefox will display it as adjusted; that is, brighter. This is
also part of the evidence that the adjustment in Firefox, and
therefore in eog, is a bug.
GIMP displays images without an adjustment, so darker than eog for
most images.
The 'display' utility from imagemagick displays images the same as
GIMP, without any apparent adjustments.
So GIMP, display from imagemagick, and Firefox all display jpgs as slightly darker than eog, without mostly skipping over the range of values just above 0. GIMP and 'display' show most pngs as darker than eog, while Firefox displays some pngs as darker than eog while others are displayed similar but with slightly darker reds it seems.
I think all the images I've looked at had 'colorspace: sRGB' in their
properties when I looked at them with 'identify' from imagemagick or
exiftool., so if that's somehow related it doesn't seem like programs
should display images differently. They probably all had 'gamma: 0.45'
in 'identify' (though this shows up as gamma: 2.2 in exiftool I
think), so I don't think that should affect image display either.
For the unusual png that eog displays differently, none of the ways I
used to convert it caused the output to be displayed in eog the same
as the original. These methods included 'convert' from imagemagick
with and without the -strip action; convert with jpg output; ffmpeg
with png output; and GIMP exporting as png with background color and
gamma tested (so four GIMP outputs total). The reason for testing
background color was that 'png:bKGD' is part of the output from
'identify' when the -strip action isn't used with 'convert', and non-
stripped pngs are treated differently in Firefox so they could
potentially also be treated differently in eog, but as it turned out
they weren't treated differently in eog.
In 'identify's output, the original png does have very slightly
different numbers under Chromaticity, with five of eight numbers
different by 0.0001. I don't know if that's supposed to affect display
of the image at all. Under the 'Properties' subsection, either the
stripped or the nonstripped version are similar to the original image.
The output of 'identify' for the 'png:sRGB intent=<value>' property
changes each time 'identify' is run on the same file, but both the
original and the stripped version (which is displayed normally in
Firefox, unlike non-stripped) have a value of around
'intent=32500±300'. For the stripped png, 'intent=0' but the other
values under the Properties subsection are the same as the original
other than adding a 'png:bKGD' field which the stripped version
doesn't do.
In exiftool, the non-stripped png from 'convert' has the fields 'Gamma
: 2.2' and 'SRGB Rendering : Perceptual', but neither the original nor
the stripped version have these fields. It's possible that somehow, if
some fields exist eog assumes certain values for other fields, but the
reason this particular png is displayed differently in eog than other
pngs is a mystery.
As a note, comparing the way different programs display images is
easier using the zoom function in Compiz, as well as the window
transparency function to line up images.
Most images being displayed lighter in eog than in many other programs
might not be a bug; I am filing this bug report because it appears to
be one. Maybe I should have tried asking under Questions but I doubt
anyone except the package maintainers could provide a correct answer,
due to inconsistency between different programs.
I am using Ubuntu 14.10, with eog (GNOME image viewer) version 3.12.2.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/eog/+bug/1436595/+subscriptions
References